Red Sky at Night
Red sky at night
Brilliant reds, purples and oranges streak across the sky as the sun sets over Lake Huron. As the colours fade, those who have made the evening pilgrimage to watch the sun set head for home and cottage.
Mother Nature's light show system is simple: the sun's colour is determined by its position in the sky. The entire spectrum of colours makes up the sun's light. On its way through earth's atmosphere, the sun's light passes through a variety of gases and minute particles that scatter some of the blue light all over the place. These particles include oxygen, nitrogen, pollution, and clouds containing solid water, water vapor (water in gas form), ice (frozen water) and snow (water in gas form that is frozen). The other colours-red, orange and yellow-are not overly affected by their trip through the earth's atmosphere and pretty much travel straight to the ground. The sky then appears blue because the blue light is strewn across the sky. The blue light is scattered about ten times more than the red. The blue light is, in fact, scattered over and over again across the sky. The other colours, meanwhile, continue pretty much on their original path.
At sunset or sunrise, when the sun appears very low in the sky, the light has to pass through more of the air ("thicker" air) closer to the earth's surface. While more blue light is flung out, almost all of the red and yellow light remains, resulting in a tremendous burst of colour. The red, orange and yellow hues that thrill sunset viewers progress more or less in a straight line directly from the sun to human eyes.
When a great number of small dust or air pollution particles are present, the sky turns more red as these particles scatter more of the blue light. The sky will also appear extremely red after a volcanic eruption due to the airborne particles produced. If clouds are present, they, too, enhance a sunset. The clouds' water droplets act as a reflector and amplifier of the sky's red and orange shades.
Through a trick of light, while we view the sun slipping beneath the horizon, it is actually already about a diameter below the horizon. The light is bent by refraction so we are able see it from the shoreline or other sunset viewing vantage points.
Sunset Note: The phenomenon of colour scatter is known as Rayleigh Scattering, named after Lord Rayleigh who, in 1871, conducted studies to discover why the sky is blue and why sunsets are red. He discovered that when light travels through a transparent media (i.e. air), most of it travels straight forward, but a small fraction is scattered, creating either a blue sky or a vivid sunset.